The present invention relates to a knife abrasive apparatus for a rotary drum shaped cutter which will be employed in, for example, a shredding machine.
Generally, in order to shred leaf tobacco into cut tobacco for cigarettes, a tobacco shredding machine is used wherein laminated leaf tobacco is transferred to a shredding port formed at an exit of two converging press conveyors while compressing it by said conveyors, and after passing therethrough, the laminated leaf tobacco is shredded by a rotary drum shaped cutter having a knife edge which moves on a virtual cylindrical outer surface (hereinafter referred to as "blade edge cylinder") proximate to the shredding port.
In the above tobacco shredding machine, an abrasive apparatus is provided separately from the rotary drum shaped cutter in order to grind the knife blade edge during operation, so that the edge will be fit for high speed processing for a long time. Also, in order to maintain a gap between the blade edge cylinder and the shredding port constant, the knife is continuously or intermittently sent out by a very small amount at a time in synchronism with the rotation of the rotary drum shaped cutter in order to compensate for the length ground, and thus the diameter of the blade edge cylinder is always maintained constant.
In general, there are two abrasive systems; one is a wet type abrasive system in which an abrasive oil is supplied to the surface of the abrasive wheel for the purposes of prevention of heating, and discharge of abrasive grains worn out as well as chips ground by the abrasive grains, and the other is a dry type abrasive system in which the grinding is done by supplying no oil. In the tobacco shredding machine described, the dry type abrasive system is usually employed in order to prevent a decrease in the quality (aroma or taste, or physical property of a final product) of shredded tobacco due to possible attachment of the abrasive oil to leaf tobacco and shredded tobacco.
In the dry abrasive system, the grain size of the abrasive grain is made coarse in order to prevent the heating of the grindstone surface or to discharge the abrasive grain worn out and chips. Because of the foregoing, in an abrasive apparatus employing said dry type abrasive system, the blade edge of a knife ground is often caused to be serrated to such a degree as to be visually observable with the naked eye.
For the purposes of reducing the losses of raw material at a time when it is shredded as much as possible, the applicant of the present patent application suggested in Japanese Patent Application Post-Examination Publication No. 56(1981)-17910 a tobacco shredding machine equipped with a rotary drum shaped cutter wherein the knife is formed in a shape of a cylinder partly diagonally cut, and the knife blade edge is disposed at a predetermined helical angle with respect to the outer peripheral surface of the drum. However, when the above-mentioned abrasive apparatus is applied to this, the serrated blade edge of the knife causes the raw material to be sewn into too tiny grains as to make meaningless the predetermined helical angles (for slicing the raw material in order to minimize the losses thereof) at which the knife blade edge is disposed to the outer peripheral surface of the drum.
The present invention was accomplished in view of the above.